1. Field of the Invention
The present invention generally relates to a data channel transmission method and apparatus for a wireless communication system operating in a dynamic Time Division Duplex (TDD) mode.
2. Description of the Related Art
Orthogonal Frequency Division Multiplexing (OFDM) is a technique for transmitting data using multiple carriers, i.e. a multi-carrier transmission scheme, which converts a serial symbol stream to parallel symbol sets that are transmitted on the orthogonal multiple carriers.
The OFDM technique began in the late 1950's with the Frequency Division Multiplexing (FDM) for military communication purposes, and OFDM using orthogonal overlapping multiple subcarriers was later developed but initially was not widely used due to the difficulty of implementing orthogonal modulations between multiple carriers. However, with the introduction in 1971 of the use of a Discrete Fourier Transform (DFT) for implementation of the generation and reception of OFDM signals, by Weinstein, the OFDM technology has rapidly developed. Additionally, the introduction of a guard interval at the start of each symbol and use of cyclic prefix (CP) overcomes the negative effects caused by multipath signals and delay spread.
Due to these technical advances, the OFDM technology is now applied in various digital communications fields such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless Local Area Network (WLAN), and Wireless Asynchronous Transfer Mode (WATM), based on the introduction of various digital signal processing technologies such as Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT).
OFDM is similar to FDM but is much more spectrally efficient for achieving high-speed data transmission by orthogonally overlapping multiple subcarriers. Due to the spectral efficiency and robustness to the multipath fading, OFDM has been considered as a prominent solution for improved broadband data communication systems. Other advantages of OFDM are to control the Inter-Symbol Interference (ISI) using the guard interval and reduce the equalizer complexity in view of hardware as well as spectral efficiency and robustness to the frequency selective fading and multipath fading. OFDM is also robust to noise impulses and thus may be employed in various communication systems.
In OFDM, modulation signals are located in two-dimensional time-frequency resources, which are divided into different OFDM symbols and are orthogonal with each other. Resources on the frequency domain are divided into different tones, and are also orthogonal with each other. That is, the OFDM scheme defines one minimum unit resource by designating a particular OFDM symbol on the time domain and a particular tone on the frequency domain, and the unit resource is called a Resource Element (RE). Since different REs are orthogonal with each other, signals transmitted on different REs can be received without causing interference to each other.
A physical channel is defined on the physical layer for transmitting modulation symbols obtained by modulating one or more coded bit sequences. In an Orthogonal Frequency Division Multiple Access (OFDMA) system, a plurality of physical channels can be transmitted depending on the usage of the information sequence or receiver. The transmitter and receiver negotiate the RE on which a physical channel is transmitted, which is a process called mapping.
High-speed, high-quality wireless data services are generally hindered by the channel environment, which suffers from frequent changes due to additive white Gaussian noise (AWGN) and power variation of received signals, caused by such instances as a fading phenomenon, shadowing, a Doppler effect from terminal movement and a frequent change in terminal velocity, and interference by other users or multipath signals. Therefore, in order to support high-speed, high-quality wireless data services, there is a need to efficiently overcome the above channel quality degradation factors.